1. Field of the Invention
This invention pertains to the field of water treatment and to the use of ion (anion) exchange resins in processes to remove oxyanion contaminants, such as perchlorate ion contaminants, from aqueous streams. These aqueous streams range from domestic, industrial and agricultural water supplies such as drinking water to waste waters, brines and other aqueous flows. More particularly, in preferred embodiments, this invention relates to improvements in methods for biologically removing perchlorate load from perchlorate-loaded ion exchange resins generated in such processes so as to permit reuse or safe disposal of the resins.
2. Background Information
Ammonium perchlorate has been used for the past 50 years as an oxidizer component in solid explosives and solid propellants for rockets, missiles and fireworks. It is estimated that well over 90% of the ammonium perchlorate produced in the United States is used in these applications. Casual handling of perchlorates and perchlorate-laden effluents by manufacturers and the build up of poorly-contained stockpiles of outdated missile and rocket fuels have resulted in perchlorate contamination of surface water and ground water supplies. Perchlorate contamination has been detected in most states of the United States (Urbansky, Urbanksy, E. T. 1998-Bioremediation Journal, 2, 81-95) and in Europe as well. It is particularly critical in the Western region of the United States.
Recently, the National Academy of Sciences (NAS) has evaluated the existing toxicological information on perchlorate and has recommended a reference dose (RfD) for perchlorate that corresponds to a Drinking Water Equivalent Level (DWEL), of 24.5 μg/L (USEPA, 2005 http://www.epa.gov/perchlorate, last reviewed: Feb. 22, 2005).
The California Department of Health Services has established an action level for perchlorate of 6 ug/l. This is based upon the potential for perchlorate to inhibit the uptake of iodine by the thyroid gland. Perchlorate levels of up to several hundred ug/l have been found in ground water in California and other states.
Two approaches to removing perchlorate from water supplies are being researched extensively—biological destruction (see Logan et al. (2001) Applied and Environ. Microbiology, 2499-2506, Hatzinger et al. (2000) In: Case Studies in the Remediation of Chlorinated and Recalcitrant Compounds, Battelle Press, 115-122, Liu, J. and J. Batista (2000). In: Bioremediation of Inorganic Contaminants, Battelle Press (6) 9: 265-273, Herman, D. and Frankenberger (1999) Journal of Environmental Quality, 28:10-18-1024, Kim K. and B. Logan (2001) Water Research, 35:3071-3076) and ion exchange (Gu et al. (2000) Environmental Science and Technology, 34:1075-1080, Batista et al., (2000), In: Perchlorate in the Environment, Kluwer Plenum, 13:135-145, Tripp, A. and D. Clifford, 2000, In: Perchlorate in the Environment, Kluwer Plenum, 12:123-134, Guter, G. (2000) In: Perchlorate in the Environment, Kluwer Plenum, 11:109-122, (Gu et al. (2001) Environmental Science and Technology, 35:3363-3368.
Biological destruction using various bacterial strains has been described at the Federal Remediation Technologies Roundtable General Meeting held on May 30, 2001 where Jeffrey Marqusee described how biological organisms could attack perchlorate in subsurface environments. Similar studies were also reported at that meting by Paul Hatzinger (Poster Number 43) and by John D. Coates (Poster Cleanup CU 45).
Ion exchange is an attractive method for removing perchlorate from water sources because perchlorate has a very high affinity for both polystyrene and acrylic-based strong base anion exchange resins. However, state of the art practice does not provide a practical and convenient method for regeneration of the resin after it has been used. This is due at least in part to perchlorate's affinity for the common resins being so strong that very large quantities of concentrated sodium chloride brine are required to displace the perchlorate during regeneration. Several hundred pounds of sodium chloride regenerant per cubic foot of resin at salt concentrations of from 6% to saturation are typically used.
These regeneration difficulties have led to an alternative ion exchange process in which the resin is used once for the adsorption of perchlorate and other oxyanions (i.e. nitrate, arsenate, sulfate) and then thrown away instead of being regenerated and reused.
In both of these processes of the prior art, a difficult-to-deal-with perchlorate-loaded spent resin is formed. The loaded resin can not be safely discarded in ordinary land fills and the like because of fears of its perchlorate content reentering the environment.
Attempts to bacterially break down the perchlorate content of the concentrated sodium chloride brines formed in conventional regeneration of perchlorate-loaded resins have been unsuccessful. This is because the bacteria are generally inactivated or killed by the high salt levels. High salt levels create an osmotic imbalance in cells containing normal levels of cytoplasmic solutes. This imbalance leads to a loss of water from the bacteria cells and an irreversible retraction of the cytoplasm, which is the cause for the rapid killing of microorganisms which are not salt-tolerant by nature. There have been several reports of negative effects of salinity on the biological reduction of perchlorate when salt concentrations exceed 3% (Gingras and Batista, 2002. J. Env. Monit., 4:96-101; Okeke et al., (2002). Env. Pollution, 118:357-63; Logan et al. (2001)., Water Research, 35:3034-3038). Gingras and Batista, supra, reported that as little as 0.5% sodium chloride present in a bioremediation environment lowered perchlorate degradation activity by 30% while 1.0% sodium chloride reduced activity by 60%.
In 2003, it was recognized by Gerald A. Guter and coworkers at Basin Water, Inc. that what was needed was a process for removing perchlorate from perchlorate-loaded ion exchange resins that did not involve the generation of large amounts of intractable perchlorate-rich regeneration products. Their PCT patent application number PCT/US2004/021467 disclosed a new biological process for removing perchlorate load from spent ion exchange resins that had been employed in perchlorate remediation settings. It also described an overall integrated ion exchange process for removing perchlorate contamination from water sources and regenerating the used ion exchange resin by biologically removing perchlorate load from it. While their processes, which involved biologically treating the perchlorate-loaded resin itself to directly break down the perchlorate load to nonperchlorate species such as chloride that pose reduced environmental burdens, was a significant advance, further studies have now shown that these processes can be improved in various manners to increase their efficiency and performance.
What is needed, and what this invention provides, are improved ion exchange processes for removing perchlorate from perchlorate-contaminated aqueous streams as well as improved biological processes for removing perchlorate load from used perchlorate-removing ion exchange resins which do not generate large quantities of intractable regeneration products. Furthermore, this invention provides new processes wherein exchange resin loading with perchlorate and biological regenerating of the resin to remove the resulting perchlorate load can occur concomitantly.